The invention disclosed herein relates to automatic track handover for automatic target tracking systems on track-while-scan surveillance sensors where the surveillance area is divided into regions which touch.
In its most general sense the invention can be applied to any automatic tracking system for a surveillance sensor whose surveillance area is divided into touching regions where each region has a separate data collection time. The invention also applies to surveillance sensors which have multiple surveillance areas where each area consists of single or multiple regions which touch. A region is defined as the extent of the field of view of a surveillance sensor during the time it gathers data for either or both coherent and incoherent processing. Wide area surveillance is achieved by arranging regions such that one region will abut another.
In providing a background discussion of track handover, reference will be made to the case where the regions are divided in azimuth and the tracking operation is based on recursive estimation. The regions could equally be divided by range. The example of division by azimuth is particularly applicable to operation of an over-the-horizon radar system which achieves very wide area surveillance by abutting a number of regions, each region being formed by a number of beams.
The presence of a target is determined by signal to noise considerations after signal processing to enhance the target feature. For a particular target model, a tracking filter calculates the predicted target position in, for instance, range and bearing. The position calculation is at the time associated with the sensor's region data. The predicted position for each target is used to search the sensor's data for candidate target measurements. Once the measurements are selected they are used to update the tracking filter's target state estimate.
Target state estimates are maintained in data blocks in solid state memory. The data blocks are arranged to minimise the amount of memory space that must be accessed when updating target state estimates.
The target state estimate is a vector which consists of component estimates derived from either directly or indirectly measured parameters of a distinct object. For example, a radar may make measurements in range and bearing and the state estimate may contain the components of range, range-rate, bearing and bearing-rate. At any given time the estimated position of a target is a function of the latest measurement and the weighted effect of previous measurements.
When the track position approaches the boundary of a region which touches an adjoining region, the effect of sensor measurement scintillation causes the sensor to produce target measurements in the adjoining region. If no allowance is made for the same target to give measurements from different regions, duplicate tracks on the same target can result and the tracking errors can increase when the target approaches the boundary. This is particularly evident for targets which travel along the edge of touching regions.
Another complication associated with tracking systems for surveillance areas subdivided into touching regions is the processing overheads for sorting and selected tracks. This invention includes an approach which minimises these overheads for surveillance sensors having large track capacities, i.e. greater than 1000.
It is the intended object of this invention to alleviate one or more of the above mentioned problems or at least provide a useful alternative.